Eye Tracking the Effects of Fine Particle Matter

Chronic exposure to fine particulate matter (PM_2.5) is a well-established driver of systemic neuroinflammation. In highly polluted metropolises like Metropolitan Mexico City (MMC), citizens are exposed to pollutant concentrations far exceeding annual safety standards from the time they are in utero. Forensic and imaging data reveal that this severe air pollution triggers early neural proteinopathies (associated with Alzheimer’s and Parkinson’s diseases) and targeted brain atrophy in young, seemingly healthy individuals. However, detecting these neurodegenerative processes before clinical cognitive deficits manifest remains a diagnostic challenge.

Measuring Oculomotor Abnormalities in Polluted Cities

In their prospective study, Lilian Calderón-Garcidueñas and her colleagues (2026) explored whether non-invasive eye-tracking metrics could expose early subclinical neurodegeneration. The study evaluated 80 clinically healthy volunteers from MMC and Cuernavaca , with 45 MMC participants also receiving high-resolution structural T1-weighted brain MRIs. It is important to note that while MMC residents are exposed to over 10 times higher concentrations of PM_2.5 compared to those from Cuernavaca, the levels in Cuernavaca still exceed levels considered to be safe.

To capture potentially subtle alterations in eye movement function, and allow testing to be undertaken in multiple locations, the researchers used an SR Research EyeLink Portable Duo eye tracker. 

Participants completed five distinct oculomotor tasks including fixation stability, smooth pursuit, and gap, step, and overlap prosaccade/antisaccade variants. The EyeLink Portable Duo was used to record from both eyes a sampling rate of 1000 Hz, allowing a very detailed analysis of oculomotor function

High Exposure Oculomotor Abnormalities

While most oculomotor measures were equivalent across the MMC and Cuernavaca cohorts, a more nuanced analysis revealed some striking oculomotor abnormalities in highly exposed MMC residents.

• Fixation Instability: Intrusive saccades, including Square Wave Jerks (SWJs) were highly prominent in pollution-exposed youth—such as a 14-year-old girl displaying 156 intrusive saccades during basic central target fixation.
• Smooth Pursuit Impairments: MMC residents frequently demonstrated abnormal antisaccade control (inhibitory control failures) and low-gain smooth pursuit containing large numbers of saccadic intrusions.
• MRI Brain Atrophy Correlations: Crucially, these, and other oculomotor metrics strongly correlated with structural brain deterioration. For example, longer saccadic latencies or poor pursuit tracking mapped directly onto volume losses in executive control and memory regions, including the fronto-temporo-parietal cortices, hippocampus, amygdala, thalamus, and cerebellum.

Portable Oculomotor Test Batteries

This research demonstrates the potential that compact, easy to administer oculomotor test batteries have as a non-invasive tool to screen, monitor, and measure the progressive impact of environmental pollution on neurodevelopment and early neurodegeneration. In the researcher’s own words: “…neurodegenerative disorders that result in early focal, and latter diffuse pathology, commonly manifest eye movement abnormalities, creating a window not only to the brain, but also to pathological processes that affect it.”

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